1. Field of the Invention
The present invention relates to the cleavage of the silicon-to-carbon bond by means of hydrogen halide, with the formation of a silicon-to-halogen bond. The carbon atom bound to the silicon in this case is a component of an alkyl group, so that by means of this method it is possible to prepare halogen alkyl silanes from alkyl silanes.
2. Discussion of the Prior Art
It is known in the case of tetraalkyl silanes to cleave a silicon-to-carbon bond by means of hydrogen halide by using Friedel-Crafts catalysts, especially anhydrous aluminum chloride. The use of this catalyst, however, has several disadvantages. Aluminum chloride is soluble in the chloralkyl silanes, so that the reaction has to be followed by a separation of the catalyst from the reaction product. Separation by distillation runs into difficulties because the catalyst remains as a sludge in the sump of the distillation apparatus and, as the distillation progresses, it constantly leads to clogging due to sublimation. Consequently, in this method of procedure, yields of pure product are obtained which amount to only about 62 percent.
The filtration of the aluminum chloride also runs into difficulties. Consequently, it has also been previously proposed to precipitate it as a complex compound with phosphorus hydroxychloride and then filter it out. This procedure is difficult and requires two additional steps.
It is an object of this invention, therefore, to provide a process for the replacement of an alkyl group of an alkyl silane by a halogen, which process can be readily performed to directly provide the desired product in a high yield, especially a yield of more than 90 percent of haloalkyl silane. More especially, it is an object of this invention to provide a process for the preparation of haloalkyl silanes, especially chloralkyl silanes where the product can be obtained without extensive recovery procedures to separate out the desired product from the reaction medium.